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#include <bits/stdc++.h>
using namespace std;

const int MAXX = 1e5+5;
const int INF = 1e9+5;
int tab[MAXX];
int pom[MAXX];

int main()
{
	int n;
	cin >> n;
	for (int i=0; i<n; i++)
		cin >> tab[i], pom[i] = tab[i];
	
	int res1=0, res2=0;
	for (int i=1; i<n; i++)
	{
		if (i % 2 == 0 && tab[i] <= tab[i-1]) tab[i] = INF, res1++;
		if (i % 2 == 1 && tab[i] >= tab[i-1]) tab[i] = -INF, res1++;
	}
	
	for (int i=1; i<n; i++)
	{
		if (i % 2 == 0 && pom[i] >= pom[i-1]) pom[i] = -INF, res2++;
		if (i % 2 == 1 && pom[i] <= pom[i-1]) pom[i] = INF, res2++;
	}
	
	
	cout << min(res1, res2);
	return 0;
}